PROJECT SUMMARY People who inject drugs (PWID) experience some of the greatest addiction-related harms and yet are under- represented in substance use treatment. A number of individual and structural barriers have been shown to prevent PWID from engaging in treatment. Many of these barriers can be reduced by low-threshold treatment approaches, but there has been very little research evaluating low-threshold treatments for PWID, especially treatments that target the mechanisms driving problematic drug use. The proposed study seeks to extend ongoing research of a behavioral addiction intervention, Behavioral Activation (BA) for substance use, by offering BA as a low-threshold intervention to non-treatment-seeking PWID. BA has demonstrated efficacy as a supplement to traditional substance use treatment, but it may also be a particularly appropriate therapy for non-treatment-seeking PWID because it targets environmental reward deficits, which are thought to be a driver of substance use, and it aims to bolster motivation for recovery by increasing engagement in value based substance-free activities. Additionally, it has high potential for cost-effective dissemination through support workers without formal training in psychotherapy, making it a very practical approach for reaching underserved substance users. The proposed study has three aims. Aim 1 will examine the feasibility and acceptability of BA for non-treatment-seeking PWID recruited from a syringe exchange program (SEP). Aim 2 will focus on developing and piloting the treatment manual through an iterative process. Aim 3 will examine the preliminary efficacy of the treatment from baseline to a 1 month follow-up using a small randomized controlled trial. This study would be the first to examine the use of this treatment in a sample of out-of-treatment substance users. If effective, this treatment approach could be implemented in community-based settings where PWID already access services, such as SEPs. This would fill an important gap in services for high-risk substance users, especially those who are interested in receiving help but are not ready to enroll in traditional substance use treatment.